1. Field of the Invention
The presently disclosed subject matter relates to a mirror driving device and a mirror driving method, and in particular to a structure of a mirror device suitable for an optical deflector used in optical scan and a drive control technique of the mirror device.
2. Description of the Related Art
Examples of a deflector configured to scan a light beam in an optical scanning device include a polygon mirror and a galvanometer mirror. However, configurations of the examples have a structure where a mirror is rotated by an electromagnetic motor, which results in constraint of size reduction. Further, in order to obtain an image with a further high resolution or realize high-speed printing, rotation of the mirror must be made further fast, which results in a problem of durability of a bearing, or heat generation or noises due to draft loss.
Recently, an oscillation mirror (MEMS (Micro Electro Mechanical System) scanner) has been proposed (Japanese Patent Application Laid-Open No. 2008-257226 and Japanese Patent No. 4092283). The oscillation mirror utilizes a silicon micromachining (MEMS) and is obtained by integrally forming a fine mirror and a beam configured to support the fine mirror on a silicon substrate. Since the oscillation mirror is configured to be oscillated reciprocally utilizing resonance, the oscillation mirror can reduce nose in spite of a high-speed operation. Further, since driving force for rotating a mirror part is small, power consumption can be suppressed. Further, the MEMS scanner has such a merit that a movable part and a driving part can be integrally manufactured from a semiconductor substrate using a MEMS processing technique.
Examples of a driving system for the MEMS scanner include a driving system utilizing a deformation of a piezoelectric body. This driving system has such a merit that torque is large and a voltage is low. Japanese Patent Application Laid-Open No. 2008-257226 discloses a structure where a mirror part is connected to a piezoelectric unimorph cantilever via a twisting hinge. By driving this piezoelectric unimorph cantilever in a direction of twisting a torsion bar, the mirror part is rotationally driven, thereby realizing one-dimensional scan. Here, by causing frequency of a driving source to coincide with a resonance frequency of a movable mirror, a large mirror rotation angle can be obtained with a lower voltage.
A part for performing resonance scan with a relatively high frequency can be incorporated into a movable frame, and the movable frame can be connected to another actuator via a twisting hinge. Thus, two-dimensional drive can be performed by rotationally driving the movable frame about an axis perpendicular to a rotational axis of the resonance scan. This technique is applied to a display or the like (Japanese Patent No. 4092283).